The present invention relates to a photoconductor, an image forming apparatus, an image forming method and a process cartridge using the same. The present invention is also directed to a method of preparing a photoconductor.
In recent years, with an increasing demand for reproduction of image information with a high definition, image forming with higher definition and resolution is highly required. In high resolution image forming, characteristics of a photoconductor are likely to be reflected in a formed image in addition to the image information itself. An image forming process employing coherent light such as laser beam for writing light is widely used in a field of electrophotography for forming a digital image, for example in copying machines, printers and facsimiles. In such a process, there tends to arise a problem of occurrence of interference fringes in a formed image due to interference of coherent light in a photoconductor.
It is known that when the photoconductor meets with the following relation:
2nd=mxcex
(wherein n is a reflective index of a charge transporting layer, d is a thickness of the charge transporting layer, xcex is a wavelength of the writing light and m is an integer), the writing light is enhanced to cause interference fringes.
For example, when xcex=780 nm and n=2.0, a set of interference fringes is generated every time the thickness of the charge transporting layer is changed by 0.195 xcexcm. In order to eliminate such interference fringes completely, therefore, the charge transporting layer should have a thickness variation not greater than 0.195 xcexcm all over the image forming area. However, it is very difficult to produce such a photoconductor for an economical reason. Thus, various methods for restraining interference fringes have been proposed.
For example, Japanese Laid-Open Patent Publication No. S57-165845 discloses a photoconductor having a charge generating layer containing amorphous Si, wherein a light absorbing layer is provided on a surface of an aluminum support to prevent mirror reflection of light on the surface of the support, thereby preventing occurrence of interference fringes. This method is effective to a photoconductor having a layer structure consisting of an aluminum support/a charge transporting layer/a charge generating layer such as an amorphous Si photoconductor but is not very effective to a photoconductor having a layer structure consisting of an aluminum support/a charge generating layer/a charge transporting layer as seen in many organic photoconductors.
Japanese Laid-Open Patent Publication No. H07-295269 discloses a photoconductor having a layer structure consisting of an aluminum support/an under coat layer/a charge generating layer/a charge transporting layer, wherein a light absorbing layer is provided on the aluminum support to prevent interference fringes. However, even with this photoconductor, it is impossible to prevent interference fringes completely.
Japanese Examined Patent Publication No. H07-27262 discloses an image forming apparatus having a photoconductor including a cylindrical support having a convex shape obtained by superimposing a sub-peak on a main peak in a cross-section cut along a plane including the central axis thereof, and an optical system for irradiating coherent light with a diameter smaller than one cycle of the main peak to the photoconductor. The image forming apparatus can restrain interference fringes to a large extent with some limited types of photoconductors. However, many of photoconductors including a support having a convex shape obtained by superimposing a sub-peak on a main peak in a cross-section cut along a plane including the central axis thereof still generate interference fringes.
A photoconductor including a support having a specified parameter of surface roughness is proposed (for example, Japanese Laid-Open Patent Publication No. H10-301311). The photoconductor can restrain interference fringes when used in an image forming apparatus having a low resolution. However, in the case of an image forming apparatus having a high resolution, it is impossible to determine conditions to eliminate interference fringes completely even though the surface roughness of the support is specified with conventionally used parameters (maximum height roughness (Ry), ten point-average roughness (Rz), center line-average roughness (Ra) etc.).
A photoconductor in which surface roughness of an intermediate layer and surface roughness of an outermost layer are specified in addition to surface roughness of a support is also known. For example, Japanese Laid-Open Patent Publication No. H6-138685 discloses a photoconductor including a conductive support having an Rz of 0.01-0.5 xcexcm and a surface protective layer having an Rz of 0.2-1.2 xcexcm. However, a surface protective layer is generally poor in hole transferring ability so that the photoconductor tends to cause a problem of an increase in electric potential of a latent image and to produce an unclear image by influences of ion species generated by electrification, oxidizing or reducing gas, humidity and so on. Also, it is extremely difficult to specify an Rz to eliminate interference fringes completely. When the writing light of the image forming apparatus has a high resolution, image defects such as interference fringes tends to occur.
Japanese Laid-Open Patent Publication No. H7-13379 discloses a photoconductor including an intermediate layer having an Rz of not greater than 1.0 xcexcm and a surface protective layer having an Rz of not greater than 1.0 xcexcm, for the purpose of preventing interference fringes such as moire. It is thought to be effective to provide the surfaces of the layers with roughness in a certain degree or greater. However, an upper limit of the Rz for each layer is disclosed but an Rz necessary to prevent interference fringes such as moire is not disclosed.
Japanese Laid-Open Patent Publication No. H08-248663 discloses a photoconductor including a support having a surface roughness of 0.01 to 2.0 xcexcm, an outermost layer having a surface roughness of 0.1 to 0.5 xcexcm and containing inorganic particles having an average particle diameter of 0.05-0.5 xcexcm. However, it is not specified what kind of surface roughness is the surface roughness of the support and the outermost layer. As mentioned above, conventional parameters of surface roughness include Ry, Rz and Ra. It is well known that even if one solid surface is measured for the surface roughness, the measurements are largely varied depending upon the parameters and upon the measurement conditions such as measurement length. Even if the roughness of the support and the outermost layer is Rz provided in JIS and so on, there are many cases where interference fringes cannot be prevented completely.
As mentioned above, conditions to prevent interference fringes completely are unknown but interference fringes are frequently reduced when a support, an intermediate layer or an outermost layer has a roughened surface. However, it is impossible to obtain a photoconductor capable of preventing interference fringes completely even if surface conditions of a support, undercoat layer (intermediate layer) and an outermost layer of a photoconductor are specified with conventionally used parameters of surface roughness, and this tendency increases as the resolution of a printed image becomes higher.
It is, therefore, an object of the present invention to provide an image forming apparatus which has overcome the problems of the prior arts.
Another object of the present invention is to provide an image forming apparatus of the above-mentioned type which is capable of producing a high-quality image free from image defects such as interference fringes, streaks, and black spots.
It is a further object of the present invention to provide an image forming apparatus capable of producing a high-quality image free from image defects such as blur without lowering the resolution of an output image.
It is a further object of the present invention to provide an image forming apparatus capable of producing a high-quality image free from image defects such as white voids, non-uniformity, discharge breakdown and interference fringes.
It is a further object of the present invention to provide an image forming apparatus in which surface conditions of a photoconductor are hardly changed even though image forming is repeated and thus no potential variation of a latent image caused by nonuniformity in electrification and sensitivity is generated and which can produce a high-quality image free from image defects such as interference fringes and black spots caused by discharge breakdown.
It is yet a further object of the present invention to provide a photoconductor capable of producing a high-quality image free from image defects such as interference fringes.
It is a further object of the present invention to provide a process cartridge having mounted thereon the above photoconductor.
It is a further object of the present invention to provide a method of preparing a photoconductor capable of producing a high-quality image free from image defects such as interference fringes.
In accordance with one aspect of the present invention, there is provided an image forming apparatus comprising a photoconductor having a photoconductive layer provided on a support, and an exposing device for irradiating a surface of said photoconductor imagewise with a coherent light to form an electrostatic latent image thereon, the surface of said photoconductor having such characteristics as to provide I(S) of at least 3.0xc3x9710xe2x88x923, wherein I(S) is given by the following equations:                               I          ⁡                      (            S            )                          =                              (                          1              N                        )                    ⁢                                    ∑                              n                =                0                                            N                -                1                                      ⁢                          xe2x80x83                        ⁢                          {                              S                ⁡                                  (                                      n                                                                  N                        ·                        Δ                                            ⁢                                              xe2x80x83                                            ⁢                      t                                                        )                                            }                                                                                    S            ⁡                          (                              n                                                      N                    ·                    Δ                                    ⁢                                      xe2x80x83                                    ⁢                  t                                            )                                =                                    1              N                        ·                                          "LeftBracketingBar"                                  X                  ⁡                                      (                                          n                                                                        N                          ·                          Δ                                                ⁢                                                  xe2x80x83                                                ⁢                        t                                                              )                                                  "RightBracketingBar"                            2                                      ⁢                  xe2x80x83                                                  X          ⁢                      (                          n                                                N                  ·                  Δ                                ⁢                                  xe2x80x83                                ⁢                t                                      )                          =                              ∑                          m              =              0                                      N              -              1                                ⁢                      xe2x80x83                    ⁢                                    x              ⁡                              (                                                      m                    ·                    Δ                                    ⁢                                      xe2x80x83                                    ⁢                  t                                )                                      ⁢                          exp              ⁡                              (                                                      -                    ⅈ2                                    ⁢                                      xe2x80x83                                    ⁢                                      π                    ·                                          n                                                                        N                          ·                          Δ                                                ⁢                                                  xe2x80x83                                                ⁢                        t                                                              ·                    m                    ·                    Δ                                    ⁢                                      xe2x80x83                                    ⁢                  t                                )                                                        
wherein
N is a number of samples obtained from a sectional curve of the surface of the photoconductor and is 2p where p is an integer,
xcex94t is a sampling interval, in xcexcm, at which the N-number of the samples are sampled, said sectional curve being obtained by measuring a profile of the surface through a preset length Nxc2x7xcex94t,
x(t) is a height of the sectional curve, in xcexcm, of a sample at a position t in said preset length, and
n and m are integers.
In another aspect, the present invention provides an image forming method wherein a coherent light is irradiated on a photoconductor having a photoconductive layer provided on a support to form an electrostatic latent image thereon, the surface of said photoconductor having such characteristics as to provide I(S) of at least 3.0xc3x9710xe2x88x923, wherein I(S) is given by the following equations:                               I          ⁡                      (            S            )                          =                              (                          1              N                        )                    ⁢                                    ∑                              n                =                0                                            N                -                1                                      ⁢                          xe2x80x83                        ⁢                          {                              S                ⁡                                  (                                      n                                                                  N                        ·                        Δ                                            ⁢                                              xe2x80x83                                            ⁢                      t                                                        )                                            }                                                                                    S            ⁡                          (                              n                                                      N                    ·                    Δ                                    ⁢                                      xe2x80x83                                    ⁢                  t                                            )                                =                                    1              N                        ·                                          "LeftBracketingBar"                                  X                  ⁡                                      (                                          n                                                                        N                          ·                          Δ                                                ⁢                                                  xe2x80x83                                                ⁢                        t                                                              )                                                  "RightBracketingBar"                            2                                      ⁢                  xe2x80x83                                                  X          ⁢                      (                          n                                                N                  ·                  Δ                                ⁢                                  xe2x80x83                                ⁢                t                                      )                          =                              ∑                          m              =              0                                      N              -              1                                ⁢                      xe2x80x83                    ⁢                                    x              ⁡                              (                                                      m                    ·                    Δ                                    ⁢                                      xe2x80x83                                    ⁢                  t                                )                                      ⁢                          exp              ⁡                              (                                                      -                    ⅈ2                                    ⁢                                      xe2x80x83                                    ⁢                                      π                    ·                                          n                                                                        N                          ·                          Δ                                                ⁢                                                  xe2x80x83                                                ⁢                        t                                                              ·                    m                    ·                    Δ                                    ⁢                                      xe2x80x83                                    ⁢                  t                                )                                                        
wherein
N is a number of samples obtained from a sectional curve of the surface of the photoconductor and is 2p where p is an integer,
xcex94t is a sampling interval, in xcexcm, at which the N-number of the samples are sampled, said sectional curve being obtained by measuring a profile of the surface through a preset length Nxc2x7xcex94t,
x(t) is a height of the sectional curve, in xcexcm, of a sample at a position t in said preset length, and
n and m are integers.
The present invention further provides a photoconductor comprising a support, and a photoconductive layer provided on said support, said photoconductor having such surface characteristics as to provide I(S) of at least 3.0xc3x9710xe2x88x923, wherein I(S) is given by the following equations:                               I          ⁡                      (            S            )                          =                              (                          1              N                        )                    ⁢                                    ∑                              n                =                0                                            N                -                1                                      ⁢                          xe2x80x83                        ⁢                          {                              S                ⁡                                  (                                      n                                                                  N                        ·                        Δ                                            ⁢                                              xe2x80x83                                            ⁢                      t                                                        )                                            }                                                                                    S            ⁡                          (                              n                                                      N                    ·                    Δ                                    ⁢                                      xe2x80x83                                    ⁢                  t                                            )                                =                                    1              N                        ·                                          "LeftBracketingBar"                                  X                  ⁡                                      (                                          n                                                                        N                          ·                          Δ                                                ⁢                                                  xe2x80x83                                                ⁢                        t                                                              )                                                  "RightBracketingBar"                            2                                      ⁢                  xe2x80x83                                                  X          ⁢                      (                          n                                                N                  ·                  Δ                                ⁢                                  xe2x80x83                                ⁢                t                                      )                          =                              ∑                          m              =              0                                      N              -              1                                ⁢                      xe2x80x83                    ⁢                                    x              ⁡                              (                                                      m                    ·                    Δ                                    ⁢                                      xe2x80x83                                    ⁢                  t                                )                                      ⁢                          exp              ⁡                              (                                                      -                    ⅈ2                                    ⁢                                      xe2x80x83                                    ⁢                                      π                    ·                                          n                                                                        N                          ·                          Δ                                                ⁢                                                  xe2x80x83                                                ⁢                        t                                                              ·                    m                    ·                    Δ                                    ⁢                                      xe2x80x83                                    ⁢                  t                                )                                                        
wherein
N is a number of samples obtained from a sectional curve of the surface of the photoconductor and is 2p where p is an integer,
xcex94t is a sampling interval, in xcexcm, at which the N-number of the samples are sampled, said sectional curve being obtained by measuring a profile of the surface through a preset length Nxc2x7xcex94t,
x(t) is a height of the sectional curve, in xcexcm, of a sample at a position t in said preset length, and
n and m are integers.
The present invention further provides a process cartridge freely detachable from an image forming apparatus, comprising the above photoconductor, and at least one means selected from the group consisting of charging means, image exposure means having a coherent light source, developing means, image transfer means, and cleaning means.
The present invention further provides a method of producing a photoconductor comprising forming a photoconductive layer on a support such that said photoconductor has surface characteristics providing I(S) of at least 3.0xc3x9710xe2x88x923, wherein I(S) is given by the following equations:                               I          ⁡                      (            S            )                          =                              (                          1              N                        )                    ⁢                                    ∑                              n                =                0                                            N                -                1                                      ⁢                          xe2x80x83                        ⁢                          {                              S                ⁡                                  (                                      n                                                                  N                        ·                        Δ                                            ⁢                                              xe2x80x83                                            ⁢                      t                                                        )                                            }                                                                                    S            ⁡                          (                              n                                                      N                    ·                    Δ                                    ⁢                                      xe2x80x83                                    ⁢                  t                                            )                                =                                    1              N                        ·                                          "LeftBracketingBar"                                  X                  ⁡                                      (                                          n                                                                        N                          ·                          Δ                                                ⁢                                                  xe2x80x83                                                ⁢                        t                                                              )                                                  "RightBracketingBar"                            2                                      ⁢                  xe2x80x83                                                  X          ⁢                      (                          n                                                N                  ·                  Δ                                ⁢                                  xe2x80x83                                ⁢                t                                      )                          =                              ∑                          m              =              0                                      N              -              1                                ⁢                      xe2x80x83                    ⁢                                    x              ⁡                              (                                                      m                    ·                    Δ                                    ⁢                                      xe2x80x83                                    ⁢                  t                                )                                      ⁢                          exp              ⁡                              (                                                      -                    ⅈ2                                    ⁢                                      xe2x80x83                                    ⁢                                      π                    ·                                          n                                                                        N                          ·                          Δ                                                ⁢                                                  xe2x80x83                                                ⁢                        t                                                              ·                    m                    ·                    Δ                                    ⁢                                      xe2x80x83                                    ⁢                  t                                )                                                        
wherein
N is a number of samples obtained from a sectional curve of the surface of the photoconductor and is 2p where p is an integer,
xcex94t is a sampling interval, in xcexcm, at which the N-number of the samples are sampled, said sectional curve being obtained by measuring a profile of the surface through a preset length Nxc2x7xcex94t,
x(t) is a height of the sectional curve, in xcexcm, of a sample at a position t in said preset length, and
n and m are integers.
The present inventors thought that when very minute interference fringes invisible with naked eyes are positively formed, the interference fringes are not visually recognized as a whole, and that interference fringes may be prevented when minute unevenness is provided on a surface of a photoconductor. However, when various photoconductors having a roughened surface were measured for the surface roughness thereof using the conventional parameters of surface roughness such as Rz, surface roughness having an effect of preventing interference fringe was not able to be specified.
For the purpose of properly specifying surface conditions of a photoconductor-to prevent interference fringes, the present inventors carefully observed sectional curves of photoconductors and found that a sectional curve of a surface of a photoconductor consists of a multiplicity of waves (of different wavelengths and amplitudes) and that waves having relatively small amplitudes as well as waves having large amplitudes largely influence the occurrence of interference fringes. Of the conventional parameters of surface roughness, Ry, which is a difference in height between the highest peak and the deepest valley of a measured sectional curve, cannot extract information of minute unevenness. Rz, which is a difference between an average of the height of the five highest peaks and an average of the depth of the five deepest valleys, is frequently used as a parameter representing an average unevenness of a sectional curve. However, when the number of waves consisting of a sectional curve is very large, the number of extracted waves is excessively small with the five highest peaks and the five deepest valleys, so that Rz cannot properly represent the sectional curve. Ra can properly represent magnitude of average unevenness of a sectional curve composed of only waves with large amplitudes. However, minute waves superimposed on waves with large amplitudes are cancelled in calculating Ra and thus are not reflected in Ra at all. Thus, Ra cannot properly express a sectional curve. As above, the conventional parameters express a sectional curve focusing on waves with large amplitudes without any consideration of minute waves with small amplitudes and thus cannot specify surface conditions of a photoconductor to prevent interference fringes.
The present inventors has found that it is necessary to make all the waves constituting the sectional curve of a photoconductor have a predetermined strength (power) or greater in order to attain such surface conditions of a photoconductor as to prevent interference fringes, and has accomplished the present invention.
The fact that the strength of all the waves is strong means that the entire surface of the photoconductor is largely undulated, namely sufficiently roughened. Then, intervals between interference fringes in an image can be too small to be recognized with naked eyes.